My, perhaps unorthodox, suggestion would be to get on the offensive and position it this way:
Q: How are things going with you?
A: Things are going great. I have finally taken a leap of faith I have been contemplating for a long time and started working on a startup, and I quit the job that was annoying me. Best decision of my life. Now, I did get some help - In part it was due to things deteriorating at work and in part it was due to getting an admit at another highly reputable program. Now, this bschool is still my first choice, of course but I could not pass up such opportunity. I won't have time while at school to work on my startup, so the time is now. (You want to emphasize to the school that you WILL choose them if they give you an admit - that's important to their yield number which translates into rankings; you want to signal that you are already wooed elsewhere but you are staying committed to them)
I don't think that a program would feel weaker about you as an applicant. Of course if you say - "I got fired and my life sucks" then it will be a problem. I suggest that you actually adopt the perspective and not just let it be empty words. You have nothing to lose and the time is now to work on your startup, travel, etc. Hopefully you will get into the program of your choosing and even if not, try to get your startup as far as you can because everything i wrote above is true - the time is now
Founder of GMAT Club
Just starting out with GMAT? Start here... | Want to know your GMAT Score? Try GMAT Score Estimator
Need GMAT Book Recommendations? Best GMAT Books
Co-author of the GMAT Club tests
Have a blog? Feature it on GMAT Club!
GMAT Club Premium Membership - big benefits and savings